This invention relates to an ignition timing control system for internal combustion engines and more particularly to an improved ignition timing control system that lends itself to adjustment and application to a variety of engines and engine types.
It has been known to provide a mechanical ignition timing control for internal combustion engines wherein the spark advance is adjusted mechanically in response to changes in position of the carburetor throttle valve. Such an arrangement is shown in Japanese published application SHO No. 60-30432. As shown in that application, there is an ignition advance system for an internal combustion engine as applied in an outboard motor wherein a mechanical linkage system interconnects the throttle valves of the carburetors with a rotatably journaled plate carrying a pulser coil that cooperates with a rotating magnet carried by the engine flywheel for achieving adjustment in timing. Although this type of arrangement has considerable advantages, there are also some disadvantages. For example, the rotational support for the pulser coil and the associated structure adds to both the size and weight of the engine. Also, with a mechanical system of this type it is difficult to provide the optimum ignition timing under all engine running characteristics.
To offset the deficiencies of the mechanical spark timing adjustment, it has been proposed to provide an electronic system wherein a sensor senses the condition of the throttle valves and then that sensed throttle valve condition is transmitted to an advance angle arithmetic circuit that electronically changes the advance angle (IT) of the spark timing in accordance with the angular position of the throttle valve (Th.theta.).
although the electronic system as described has a number of advantages over the mechanical system, it itself has several disadvantages. For example, if changes in tuning of the spark timing relative to the throttle position are required, it is necessary to provide a completely new electronic module or a substantial component of it. Also, this makes it difficult to change the spark timing in response to geographic characteristics or to adapt a given ignition system to engines of different types.
It is, therefore, a principal object of this invention to provide an improved ignition timing circuit for an internal combustion engine.
It is a yet further object of this invention to provide an electronic ignition timing control that provides and permits adjustment for a wide variety of factors without changing the electronic components.
it is a still further object of this invention to provide an electronic timing control system that permits simple mechanical adjustment.